Apparatus, system, and method for storage of mushrooms

ABSTRACT

A method for extending freshness of  Agaricus bisporus  mushrooms is described. In one embodiment, the method includes providing a modified atmosphere in contact with  Agaricus bisporus  mushrooms. The modified atmosphere includes from 14% to 18% by volume of oxygen and from 5% to 9% by volume of carbon dioxide.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser. No. 60/725,140, filed on Oct. 7, 2005, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention is generally related to storing mushrooms and, more particularly, is related to storing Agaricus bisporus mushrooms in a commercial retail setting while preserving characteristics typically associated with fresh mushrooms.

BACKGROUND OF THE INVENTION

Fresh-cut fruits and vegetables that are ready to be used by consumers with little or no additional processing (sometimes referred to as “value-added produce”) constitute the fastest-growing segment of the fresh produce market. In the case of mushrooms, appearance and cleanliness are two major factors used by consumers in assessing the freshness or quality of the mushrooms. To fit the definition of value-added produce, mushrooms typically require washing to remove surface debris prior to their use. However, unwashed mushrooms historically have shown better long-term storage characteristics than washed mushrooms.

Although techniques have been developed for storage of certain common fruits and vegetables, such developments have provided little guidance for mushrooms. Mushrooms, being fungi, typically have very different characteristics relative to other common fruits and vegetables found in a grocery store. In fact, mushrooms can be very different from each other, belonging to many different genera and exhibiting different patterns of growth, respiration, and other reactions under the same set of conditions. For example, shitake mushrooms belong to the genus Lentinus, and are often preserved for storage in sealed bags, as their respiration produces ethylene that acts as a preservative. Sealed bags, however, are undesirable for storing other types of mushrooms, such as a standard commercial strain Agaricus bisporus. Agaricus strains can respire to produce conditions in a sealed bag that would lead to dangerous growth of anaerobic bacteria, such as Clostridium botulinum that is associated with botulism.

Some of the problems associated with storage of mushrooms arise from their distinctive metabolism. Mushrooms can exhibit a high respiration rate and, hence, can release a considerable amount of water from metabolism. This, along with moisture added during any wash process, can contribute to rapid microbial growth as well as premature discoloration. As a result, certain types of solid (non-perforated) films used commercially for food packaging are undesirable, since these films do not allow for sufficient escape of moisture. Other types of solid films may well allow for sufficient moisture transfer, but may not provide sufficient oxygen transfer to avoid dangerous anaerobic conditions resulting from mushroom respiration. Previous attempts have also involved the use of perforated films that are provided with holes to avoid high moisture levels. Unfortunately, the presence of the holes sometimes contributed to excessive moisture loss and desiccation of mushroom tissues in proximity to the holes.

It is against this background that a need arose to develop the apparatus, system, and method for storing mushrooms described herein.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to a method for extending freshness of Agaricus bisporus mushrooms. In one embodiment, the method includes providing a modified atmosphere in contact with Agaricus bisporus mushrooms. The modified atmosphere includes from 14% to 18% by volume of oxygen and from 5% to 9% by volume of carbon dioxide.

In another aspect, the invention relates to a container for storing Agaricus bisporus mushrooms. In one embodiment, the container includes a set of walls defining an interior space and having a set of holes that are spaced to provide substantially even diffusion of respiration gases through the holes. The holes provide an air flow rate, per ounce of Agaricus bisporus mushrooms to be stored within the container, in a range of 0.2 to 0.6 Standard Cubic Foot per Hour when a pressure differential of 5 inches of water is applied.

Other aspects and embodiments of the invention are also contemplated. The foregoing summary and the following detailed description are not meant to restrict the invention to any particular embodiment but are merely meant to describe some embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the nature and objects of some embodiments of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.

FIG. 1 through FIG. 4 illustrate storage bags that can be implemented in accordance with some embodiments of the invention.

DETAILED DESCRIPTION Overview

Embodiments of the invention relate to improvements in storage of mushrooms that enhance their shelf-life, provide food safety, and preserve their appearance. Mushrooms that can benefit from these improvements include Agaricus bisporus mushrooms, whether washed or unwashed, and whether whole or sliced.

Some embodiments of the invention involve storage of fresh mushrooms in a modified atmosphere, which can be achieved through suitable management of levels of respiration gases. In some instances, management of respiration gases can involve controlling either of, or both, an oxygen level and a carbon dioxide level and, optionally, a Relative Humidity (“RH”). By way of example, preservation of fresh mushrooms can be achieved by maintaining the level of oxygen within a desired range, such as from about 10% to about 20% (by volume), by maintaining the level of carbon dioxide within a desired range, such as from about 2.5% to about 12% (by volume), and, optionally, by maintaining the RH within a desired range, such as from about 87% to about 100% (in the absence of free liquid water).

Definitions

The following definitions apply to some of the elements described with regard to some embodiments of the invention. These definitions may likewise be expanded upon herein.

As used herein, the term “set” refers to a collection of one or more elements. Elements of a set can also be referred to as members of the set. Elements of a set can be the same or different. In some instances, elements of a set can share one or more common characteristics.

As used herein, the terms “optional” and “optionally” mean that the subsequently described event or circumstance may or may not occur and that the description includes instances where the event or circumstance occurs and instances in which it does not.

As used herein, the term “fresh mushroom” refers to a mushroom that retains a set of physical characteristics substantially comparable to those present at harvest. In some instances, a fresh mushroom refers to one that has not been heated, canned, or frozen to extend shelf-life.

As used herein, the term “freshness” refers to a condition that is substantially comparable to that present at harvest. In some instances, freshness can refer to a condition that is acceptable to a consumer, such as a shopper at a retail location. Such condition can be established by customer satisfaction surveys or by quantitative standards, such as those set out in the Examples that follow.

As used herein, the term “storage” refers to a set of stages through which a mushroom passes between harvest until its consumption. These stages can include initial retention by a producer, a shipping process, retention by a retailer in a back room or on a retail shelf, and retention by a customer.

As used herein, the term “retail location” refers to a site at which mushrooms are sold directly to a consumer. An example of a retail location is a grocery store, where mushrooms are typically displayed and stored in a refrigerated setting.

As used herein, the term “substantially uncontrolled atmosphere” refers to one in which there is a substantial absence of a control process for respiration gases, other than that which can result from misting or other wetting or from refrigeration. In such substantially uncontrolled atmosphere, levels of carbon dioxide and oxygen can be substantially comparable to levels present in the earth's normal atmosphere, namely less than 1% (by volume) of carbon dioxide and approximately 21% (by volume) of oxygen. At a retail location for mushrooms, surrounding conditions may increase carbon dioxide level and reduce oxygen level to some extent, and it is contemplated that a substantially uncontrolled atmosphere encompasses such typical variations.

As used herein, the term “modified atmosphere” refers to one in which either of, or both, an oxygen level and a carbon dioxide level differ from that present in a substantially uncontrolled atmosphere or the earth's normal atmosphere. In some instances, a modified atmosphere can include less than 21% (by volume) of oxygen and more than 1% (by volume) of carbon dioxide. Optional control of RH can include providing a relatively high RH (e.g., at or above 87%) and the absence of free liquid water (e.g., water in the form of a mist or suspended droplets).

As used herein, the term “anaerobic condition” refers to an atmosphere with an oxygen level less than 2% (by volume).

As used herein, the term “respiration gases” refers to either one of, or both, carbon dioxide and oxygen, the former being generated by respiration, and the latter being consumed. Water (in the form of water vapor) can also be generated by respiration. However, as used herein, the control of respiration gases need not involve control over water vapor.

As used herein, the term “washed mushroom” refers to one that is processed to substantially remove surface debris after harvesting. In some instances, a washed mushroom can be subjected to an aqueous wash process using a set of aqueous solutions, such as including a set of agents to assist in dirt removal, preservation, bacterial suppression, or the like. An aqueous solution can include pure water or water containing dissolved or suspended agents used in a wash process. Other examples of aqueous solutions include suspensions, emulsions, and other water mixtures.

As used herein, the term “sliced mushroom” refers to one that is cut after harvesting. In some instances, a sliced mushroom can be one that is cut into smaller pieces, such that an interior of a mushroom cap or stem is exposed at a location other than an initial point where the mushroom cap or stem was separated from a mushroom bed. Cutting of mushrooms can occur after washing, although additional washing operations can also occur afterwards. In some instances, cutting of mushrooms is considered to occur after washing when at least one aqueous washing operation occurs prior to the cutting.

As used herein, the term “container” refers to any object capable of holding or retaining another object, such as a set of mushrooms. A “substantially gas-impervious” container can be one in which, in the absence of holes that allow for air flow, anaerobic conditions would occur over time (e.g., due to respiration of mushrooms and at a rate depending on temperature) if that container remains closed. A container can have an internal volume larger than a volume of mushrooms stored in the container. As such, there can be a range of relative proportion of a “mushroom storage volume,” which is a portion of the internal volume in which the mushrooms are located when the container is in a normal storage position, relative to a “void volume,” which is a portion of the internal volume substantially void of the mushrooms when the container is in the normal storage position.

As used herein, the term “hole” refers to a channel or passageway that permits flow of one or more of the following: oxygen; carbon dioxide; and water vapor. A hole can be a physical opening or perforation formed in a solid material, such as by cutting, plastic molding, or any other suitable process, or can be a pore of a porous or semi-porous membrane. In some instances, a hole can be formed in a wall of a container to provide for gas exchange between an interior and an exterior of the container.

As used herein, the term “hole pattern” refers to an arrangement of a set of holes, such as their location, number, and size. A hole pattern can include a set of holes that are spaced to provide “substantially even” diffusion of respiration gases through the holes into and out of a container. Such substantially even diffusion can allow for some variation in levels of respiration gases within a container as mushrooms respire. Unevenness of respiration gas levels can result from non-uniform packing of mushrooms, irregular contact between the mushrooms, and differences in distance from a particular mushroom to a nearest hole through which diffusion can occur (relative to other mushrooms). In the case of substantially even diffusion, individual measurements (e.g., at least 2 measurements) of respiration gas levels at different locations within a container can differ from an average value for all measurements by no more than 20%, such as no more than 10% or no more than 5%.

As used herein, the term “Standard Cubic Foot per Hour” or “SCFH” refers to a measure of air flow through a wall of a container. In particular, SCFH can be determined with reference to a “Standard Cubic Foot” or “SCF,” which is one cubic foot of air at standard conditions of temperature and pressure. Standard pressure corresponds to 1 atmosphere (variously expressed as 14.7 pounds per square inch (“psi”), 1.01325×10⁵ Pascal (“Pa”), or 760 torr), and standard temperature corresponds to 20° C. (or 68° F.). Measurements made at different temperatures and pressures can be corrected to standard conditions using the formula: P₁V₁/T₁=P₂V₂/T₂. In some instances, air flow can be measured in a RH range expected to be present in a container, such as 87% to 100%.

Wash Process

Certain embodiments of the invention can be used in conjunction with a wash process for storage of washed mushrooms. An example of a wash process is described below, although it should be recognized that a variety of other wash processes can also be used. The wash process described herein is desirable, since it can provide preservation characteristics in addition to washing. Further details related to this wash process can be found in U.S. Pat. No. 6,500,476, issued on Dec. 31, 2002, the disclosure of which is incorporated herein by reference in its entirety.

According to an embodiment of the invention, a wash process includes: (1) contacting mushrooms with an aqueous anti-microbial solution having a pH from about 10.5 to about 11.5; (2) contacting the mushrooms one or more times with an aqueous pH neutralizing buffer solution that includes an organic acid and a salt of an organic acid, wherein the solution is substantially free from erythorbic acid and sodium erythorbate; and (3) contacting the mushrooms one or more times with a solution that includes a browning inhibitor and a chelating agent.

Advantageously, the wash process can be viewed as including three distinct operational stages: (1) an anti-microbial stage; (2) a neutralization stage; and (3) an anti-browning stage. In the first stage, the wash process uses a high pH solution as an anti-microbial treatment for whole or sliced mushrooms. This treatment can significantly reduce microbial load and associated bacterial decay and browning of mushroom tissue. To reduce damage of mushroom cap tissue from exposure to the high pH solution, the wash process includes a neutralization stage that is performed following exposure to the high pH solution. The wash process also includes an anti-browning stage to address enzymatic browning. The anti-browning stage can incorporate an anti-browning solution including an anti-oxidant or browning inhibitor, such as calcium, to maintain cellular tissue and to enhance browning inhibition. Ethylenediaminetetraacetic acid (“EDTA”) can be used to provide further browning inhibition. By separating the neutralization stage and the anti-browning stage, the wash process can be more cost effective by reducing depletion of the relatively expensive anti-browning solution.

More particularly, the anti-microbial stage of the wash process can involve contacting mushrooms with an anti-microbial buffer solution having a pH from about 10.5 to about 11.5. A wide variety of compounds can be used alone, or in combination, in this solution to attain the desired pH, such as sodium bicarbonate, sodium carbonate, and sodium hydroxide. In some instances, a combination of sodium bicarbonate and sodium carbonate is desirable. About 0.3% to about 0.5% (by weight) of sodium bicarbonate and about 0.05% to about 0.10% (by weight) of sodium carbonate can be particularly satisfactory. In some instances, an initial contact with the anti-microbial buffer solution can be carried out for about 20 to about 40 seconds at an ambient temperature of about 25° C. Somewhat elevated temperatures can be used to provide greater anti-microbial action, but these elevated temperatures can permit lower dwell times in solution.

Next, the mushrooms can be contacted one or more times with at least one aqueous pH neutralizing buffer solution including an organic acid and a salt of an organic acid, while being substantially free from erythorbic acid and sodium erythorbate. This neutralization stage is carried out to reduce the pH of the mushrooms to substantially their normal pH, and can be accomplished by applying the buffer solution via any conventional means, such as by dipping, spraying, or cascading. In some instances, the buffer solution has a pH of about 3.0 to about 5.0. Acids and bases used for preparation of the salt can be weak acids and bases, such as citric acid and sodium citrate. For example, a 0.1 N solution of citric acid, having a pH of about 3.5, can be used effectively. Other examples of organic acids include malic, acetic, phosphoric, and lactic acids. Contacting time can vary, for example, with the pH of the mushrooms after the anti-microbial stage and volume of the buffer solution, and can range from about 10 to about 30 seconds.

The anti-browning stage of the wash process can involve treating the mushrooms one or more times with at least one solution including a browning inhibitor and a chelating agent. A wide variety of browning inhibitors can be used to retard the effect of tyrosinase. These browning inhibitors include reducing agents, such as sodium erythorbate, erythorbic acid, ascorbic acid, and calcium ascorbate. A wide variety of chelating agents that have a high affinity. for copper can be used. These can include, for example, polyphosphates such as sodium hexametaphosphate and others currently approved for use on fruits and vegetables and that are categorized by the Food and Drug Administration as Generally Recognized As Safe (“GRAS”). Calcium disodium EDTA can also be particularly satisfactory for certain applications. In some embodiments, the solution used in the anti-browning stage can also include calcium chloride.

In some instances, the pH of individual solutions can be monitored for the purpose of maintaining an optimum pH. Also, the concentration of sodium erythorbate can be monitored for enhancing inhibition of enzymatic browning of mushrooms.

For certain applications, the wash process can be implemented as a continuous process in which mushrooms are introduced into a first tank and conveyed through each stage with reduced damage, reduced browning, and reduced depletion of active ingredients. Solutions of sodium bicarbonate and sodium carbonate can be adjusted with sodium hydroxide to achieve a high pH in a first stage and maintained at a temperature of at least about 25° C. After the first stage, the pH of the mushrooms can be rapidly adjusted to about 6.5, which is more physiologically acceptable for the mushrooms. This rapid reduction in pH can be accomplished during a second stage of the process or as part of a rinsing operation. The rinsing operation can occur in a tank that contains a citrate buffer made from an organic acid and a salt of an organic acid and that is at ambient temperature. To reduce uptake of solution, the mushrooms can remain in the second stage for no more than about 10 to about 30 seconds. The mushrooms can then be transported by a conveyor with reduced submersion depth (e.g., to reduce uptake of solution) to a third stage. A solution used in the third stage can be maintained at ambient temperature and can include sodium erythorbate, calcium chloride, and EDTA as a treatment for enzymatic browning. The mushrooms can remain in this solution for about 20 to about 40 seconds. The total immersion or solution exposure time during the three stage process can be limited to about 50 to about 110 seconds.

Storage of Mushrooms

Certain embodiments of the invention are implemented based on a discovery by Applicants that preservation of mushrooms is enhanced by providing a modified atmosphere in contact with or surrounding the mushrooms. This modified atmosphere can involve a reduced level of oxygen and an elevated level of carbon dioxide relative to those present in a substantially uncontrolled atmosphere or the earth's normal atmosphere. For example, this modified atmosphere can include an oxygen level within a range of about 10% to about 20% (by volume), such as from about 14% to about 18% or from about 15% to about 17%, and a carbon dioxide level within a range of about 2.5% to about 12% (by volume), such as from about 5% to about 9% or from about 6% to about 8%. Optionally, this modified atmosphere can also involve controlling the RH to be in a range of about 87% to about 100%, such as from about 88% to about 94% or from about 88% to about 92% (in the absence of free liquid water).

A modified atmosphere can be achieved in a variety of ways. In some embodiments, as described further below, containers in the form of flexible storage bags or hard clam-shell packagings can be used to provide the desired modified atmosphere. This can be achieved by controlling gas flow into and out of a container by using a set of holes, by using a set of permeable or semi-permeable membranes, or both. In other embodiments, mushrooms can be sold loose so that customers can select a desired amount of mushrooms. For these embodiments, the mushrooms can be positioned in a container with a lid that automatically closes, with a modified atmosphere being pumped into the container from a compressed gas tank or from an atmospheric extraction device to maintain the desired modified atmosphere.

For example, a container can be implemented to achieve a steady-state, modified atmosphere by providing a set of holes to control the rate of gas exchange between an interior of the container and an ambient atmosphere surrounding the container. An atmosphere inside the container typically starts with normal oxygen and carbon dioxide levels and the RH of an ambient atmosphere at which mushrooms are placed into the container. The atmosphere inside the container then typically changes over time as the mushrooms respire, with the level of oxygen decreasing and the levels of carbon dioxide and water vapor increasing. Concentration gradients can develop between the interior of the container and the ambient atmosphere. These concentration gradients on two sides of the holes can cause respiration gases to diffuse through the holes. In particular, oxygen can enter to replace what has been used up by cellular respiration, while carbon dioxide and water vapor, which have accumulated as a result of cellular respiration, can exit. Eventually, steady-state levels of respiration gases can be reached inside the container, with specific levels depending on the amount of the mushrooms present to produce and use up respiration gases and an area of the holes to allow gas exchange.

To achieve desired oxygen and carbon dioxide levels while maintaining a high RH in the absence of free liquid water, a container for storage of mushrooms is typically perforated. For example, holes in the form of physical openings can be provided in a container that would otherwise restrict water vapor movement and exchange of oxygen and carbon dioxide with an ambient atmosphere. The holes can provide for sufficient replenishment of oxygen and discharge of carbon dioxide to avoid anaerobic conditions. Control of a total hole area by selecting the number and size of the holes can allow appropriate steady-state conditions to be reached. The desired steady-state conditions can also be achieved by using a permeable or semi-permeable membrane in combination with the holes.

With regard to location, size, and number of holes formed in a container, a range of variations can be used to provide satisfactory results in terms of a substantially even diffusion of respiration gases. In some instances, a hole pattern can be formed in a wall or multiple walls of a container, such that there is gas exchange between most or all interior portions of the container and an ambient atmosphere. The holes can be substantially uniformly spaced around the container. However, such uniform spacing is not required in all applications. Indeed, a range of hole patterns can be used, since diffusion of respiration gases can be relatively rapid and can account for variations in spacing of holes. In particular, a concentration gradient can develop to facilitate internally generated respiration gases to diffuse to certain ones of the holes that are located further away, while oxygen can diffuse inwardly in a similar manner. Thus, a series of holes along a line in a wall of a container (or along several lines spaced apart from each other) can provide adequate uniformity of gas exchange. Such lines of holes can be relatively easy to manufacture when the container is, for example, a flexible film storage bag. On the other hand, holes spaced in a two-dimensional array on a surface can also be satisfactory, and can be readily manufactured by a number of techniques. Many satisfactory hole patterns can space a set of holes such that a distance from any mushroom to a nearest hole is no greater than about one third of a characteristic dimension (e.g., a length) of a container, such as no more than about one fourth of the characteristic dimension. In some instances, absolute distances between a mushroom and a nearest hole can be less than about 60 mm, such as less than about 40 mm or less than about 20 mm. These distances can be maintained while varying a shape of a container or a weight of mushrooms present. In the case of larger distances, specific arrangement of interior geometry and free gas volumes (e.g., by providing shelves in a large container that provide layers of mushrooms with spaces between layers) can also provide satisfactory results.

In the absence of a forced exchange, gas exchange between an interior and an exterior of a container typically occurs via diffusion. It should be noted, however, that changing temperature and pressure can cause some expansion or contraction of an interior volume of the container, thereby creating conditions similar to a forced exchange. For some embodiments, a forced-air-flow measurement technique can be used to select a hole pattern to provide desired overall diffusion rates. Forced-air-flow measurements can be based on Graham's law of diffusion, which states that, under the same conditions of temperature and pressure, rates of diffusion for gases are inversely proportional to the square roots of their molar masses:

r ₁ /r ₂=√{square root over (M ₂ /M ₁)}.

This same formula can be used to determine relative rates of effusion, namely a process by which a gas under pressure escapes from a compartment by passing through a small opening. Accordingly, a measurement of a rate of effusion can be used to determine a rate of diffusion of a mixture of gases, as relative diffusion rates for various species of the gas mixture can be related to relative effusion rates. An actual diffusion rate for an individual species of the gas mixture is typically proportional to its measured effusion rate under specified conditions of pressure and, once measured, can be used to determine an appropriate hole pattern for mushroom storage.

An estimate of a diffusion rate satisfactory for the practice of some embodiments of the invention can be determined by measuring a rate of air flow into or out of a container with a given hole pattern and under specified pressure conditions. This flow rate can take into consideration a weight of mushrooms that will be present in the container, as larger amounts of mushrooms can produce larger amounts of respiration gases and, thus, can require a larger hole area to handle a higher diffusion rate. Using a pressure differential between an interior of a container and an ambient atmosphere of 5 inches of water (1 inch of water=2.49089×10² Pa), it has been discovered by Applicants that satisfactory results can be achieved with a flow rate in the range of about 0.2 to about 0.6 SCFH per ounce of mushrooms, such as from about 0.3 to about 0.45 SCFH per ounce of mushrooms. This desirable range can be relatively insensitive to normal variations in temperature and ambient atmospheric pressure, although it can be assumed that testing is performed at or close to standard conditions of 20° C. and 1 atmosphere. By way of example, a container can be implemented based on this desirable range (e.g., 4 mm² of open area for one standard mushroom package size) so as to have an oxygen diffusion rate on the order of, for example, 150 cubic centimeters per hour.

In some embodiments of the invention, a combination of size, number, and location of a set of holes can be selected to achieve a desired steady-state, modified atmosphere. In one such embodiment, a number and size of the holes can be selected to provide from about 0.05 to about 1.5 mm² of open area per ounce of mushrooms, such as from about 0.08 to about 0.20 mm² or about 0.125 mm² (+/−10%) of open area per ounce of mushrooms. A range of one to six holes per ounce of mushrooms, with each hole having a characteristic dimension (e.g., diameter) from about 150 to about 600 μm, can be located in a set of walls of a container. In a container designed for retail purposes, a set of holes can be located, at least in part, in a header area away from mushrooms to create a gradient of high to low RH. This gradient provides desired water vapor transmission and maintains a desired RH surrounding the mushrooms. However, a set of holes can also be located near the mushrooms, particularly in the case of a larger container where a void volume can be at a distance from the mushrooms at a bottom of the container. This combination of size and number of holes per unit weight of mushrooms (along with their location) can allow desired levels of oxygen, carbon dioxide, and RH to develop in a void volume (e.g., a headspace) of the container during storage. Diffusion within the container can ensure relatively even levels of oxygen, carbon dioxide, and RH throughout the container.

Table 1 below sets forth design parameters for containers implemented in accordance with some embodiments of the invention:

TABLE 1 Hole dimension (e.g., 150-600 μm or 200-300 μm diameter if round): Hole dimensions (e.g., 150 × 200-300 μm or 150 × 250 μm width × length if oblong): (max. ratio of 2.0 for length to width ratio) No. of holes/oz of 2-4 or 2-2.5 mushrooms: Flow rate per hole: 0.15-0.30 SCFH at a pressure of 5 inches of water Flow rate per bag: 2.0-18 SCFH at a pressure of 5 inches of water Flow rate per oz of 0.2-0.6 SCFH or 0.3-0.45 SCFH at a mushrooms: pressure of 5 inches of water

FIG. 1 through FIG. 4 illustrate storage bags 100, 200, 300, and 400 that can be implemented in accordance with some embodiments of the invention. The storage bags 100, 200, 300, and 400 are illustrated as flat polymeric films or sheets prior to folding and sealing of their edges.

Referring to FIG. 1, the storage bag 100 is implemented as a “lay-down” bag, namely one with a normal storage position that is substantially horizontal, and can hold up to about 4 ounces of mushrooms. The storage bag 100 has a hole pattern including a first set of perforations 102 and a second set of perforations 104, which are arranged in a “staggered” configuration on opposite sides of the storage bag 100 upon folding and sealing.

As illustrated in FIG. 2, the storage bag 200 is implemented as a “stand-up” bag, namely one with a normal storage position that is substantially vertical, and can hold up to about 8 ounces of mushrooms. The storage bag 200 has a hole pattern including a first set of perforations 202 and a second set of perforations 204, which are arranged in a “staggered” configuration on opposite sides of the storage bag 200 upon folding and sealing.

Similar to the storage bag 200, the storage bag 300 illustrated in FIG. 3 is implemented as a “stand-up” bag. The storage bag 300 also has a hole pattern including a first set of perforations 302 and a second set of perforations 304, which are arranged in a “staggered” configuration on opposite sides of the storage bag 300 upon folding and sealing.

Turning next to FIG. 4, the storage bag 400 is implemented as a “lay-down” bag, and can hold up to about 40 ounces of mushrooms. The storage bag 400 has a hole pattern including a first set of perforations 402 and a second set of perforations 404, which are arranged in substantially evenly spaced lines and in an “opposing” configuration on opposite sides of the storage bag 400 upon folding and sealing.

It should be recognized that the specific embodiments described above are provided by way of example, and various other embodiments are also contemplated. For example, moisture management can become a greater issue when an amount of mushrooms placed in a container exceeds a certain threshold, such as about 16 ounces (although similar considerations can also apply for smaller amounts of mushrooms). In particular, if the container is implemented as a “stand-up” bag, the mushrooms can tend to clump towards a bottom of the container, which can cause bulging and increased cross-section or density of the mushrooms within the container. This increased cross-section may not significantly impede exchange of oxygen and carbon dioxide, but can create an undesirable increase in moisture level within the package. In some instances, this increase in moisture level may not be adequately addressed by adjusting a hole pattern, without disturbing desired levels of oxygen and carbon dioxide.

According to some embodiments of the invention, two approaches can be used to address such increase in moisture level. In one approach, a container can be implemented as a “lay-down” bag so as to control a maximum depth of mushrooms within the container. In another approach, a container can be implemented using a film or a laminate of films that provide a desired Moisture Vapor Transmission Rate (“MVTR”). In this approach, a hole pattern can be formed in the film or laminate of films to maintain desired levels of oxygen and carbon dioxide. Examples of desirable films include polymeric films having a MVTR in the range of about 0.3 to about 2.0 g/m².24 hr.atm, such as from about 0.4 to about 1.5 g/m².24 hr.atm (as determined by procedures specified by the American Society for Testing and Materials). Examples of polymeric films include those formed of polyethylene, polypropylene, polyester, polylactic acid, polyethylene terephthalate, Nylon, or combinations thereof. Table 2 below sets forth specific examples of laminates that can be used to provide satisfactory results.

TABLE 2 48 gauge polyethylene terephthalate/ MVTR: 0.49 g/m² · 24 hr · atm 2 mil polyethylene 60 gauge biaxially-oriented Nylon/ MVTR: 1.12 g/m² · 24 hr · atm 1 mil polyethylene 60 gauge biaxially-oriented Nylon/ MVTR: 0.76 g/m² · 24 hr · atm 1.5 mil polyethylene 60 gauge biaxially-oriented Nylon/ MVTR: 0.58 g/m² · 24 hr · atm 2 mil polyethylene

EXAMPLES

The following examples describe specific aspects of some embodiments of the invention to illustrate and provide a description for those of ordinary skill in the art. The examples should not be construed as limiting the invention, as the examples merely provide specific methodology useful in understanding and practicing some embodiments of the invention.

Example 1

The following sets forth general protocols that were used for various tests:

Raw Material

Hybrid off-white Agaricus bisporus mushrooms were used for testing. Because of variability in commercially grown mushrooms, all tests were conducted on mushrooms produced and harvested under commercial conditions to ensure that the tests would provide results indicative of use in commercial settings. No grading was done beyond conventional protocols. However, tests were completed on a range of maturities and harvest numbers (also referred to as “break” or “flush” in the mushroom industry). Flush 1, 2, and 3 exhibited different quality and shelf-life characteristics. Testing was generally conducted using second break mushrooms. However, testing was also conducted on other breaks and quality of mushrooms to confirm that the general protocols would work on a range of mushrooms. Harvested mushrooms were stored at about 4° C. (or about 38-42° F.) prior to processing. After harvesting, the mushrooms were washed and treated as described in U.S. Pat. No. 6,500,476, and then packaged. Tests were conducted on whole and sliced mushrooms. Sliced mushrooms were prepared using a Walker slicer (Dutch Tech-Source) at a thickness of about ¼ inch and weighed into a till or a bag.

Quality Measurements

Effectiveness of different packaging for maintaining whiteness and texture was determined by measuring a degree of discoloration of mushrooms on a daily interval against a control of conventionally packaged mushrooms from the same production lot. The degree of discoloration was documented using a Minolta colorimeter model BC-10 (Konica Minolta, Mahwah, N.J.), with comparisons using the L and Y components. All measurements were taken at a center of a profile of a cut mushroom away from gill or stem tissue. Bags were sealed using an impulse sealer (Impulse Dynamics, Inc., Walnut Creek, Calif.), and packed in a corrugated shipping container to simulate commercial storage conditions.

A subjective rating scale was used to evaluate quality and shelf-life:

-   -   Overall and whiteness: 1 worse, 5 best     -   Bacterial growth: 1=heavy bacterial growth, 5=No evidence of         bacterial growth     -   Gill color: 1=very dark gills, 5=pink or very light colored         gills     -   Stem elongation: 1=extreme elongation, 5=no obvious elongation

Container Preparation

Perforated bags were manufactured from either linear low density polyethylene (1.75 mil thickness, food-service-size bags) or from a laminate (2.0 mil polyethylene and 0.48 mil polyethylene terephthalate). Holes were formed using a laser punch. Hole patterns included a number of rows (typically 3 rows per bag and typically 10 holes per row). In some instances, holes were taped over to provide a desired number of holes at a desired location in a bag. Holes were also placed at different distances from a top of a bag, as further described below. Holes were generally oblong (e.g., oval) rather than round. Hole size was generally about 150×250 μm in tests conducted in the examples below. Hole number ranged between 15 and 100 holes per bag, depending on a weight and surface area of a bag. Characteristics of resulting bags are set forth in the following Table 3.

TABLE 3 No. of Hole size Wt. of Flow/bag Flow/hole Holes (μm) Hole Pattern mushrooms (SCFH) (SCFH) 20 150 × 250 6 × 8 × 6  8 oz 3.0-3.2 .160 24 150 × 250 8 × 8 × 8 10 oz 3.3-4.0 .167 20 150 × 250 6 × 8 × 6  8 oz 3.0-3.2 .160 24 150 × 250 8 × 8 × 8 10 oz 3.3-4.0 .167 86 200 40 oz 16-17 .187

The notation “X×Y×Z” refers to three rows of holes, with X holes in a first row, Y holes in a second row, and Z holes in a third row. The hole patterns set forth in Table 3 yielded a total open area per bag of 0.4 to 4.0 mm², and exhibited a flow rate per hole between about 0.15 and about 2.0 SCFH at a pressure differential of 5 inches of water. A till that was used for comparison purposes had 61.33 mm² of open area per container.

Measurement of Respiration Gas Levels

Levels of respiration gases were measured using a PBI Dansensor Checkpoint O₂/CO₂ analyzer (Glen Rock, N.J.). A sampling area was prepared by placing a piece of tape on a bag with a dab of flexible silicone on the tape. A needle from the analyzer was inserted through the silicone for gas sampling. By following this procedure, contamination from external air was reduced.

Example 2

The following sets forth a compilation of data from a number of different perforated bags into 3 categories based on measured levels of carbon dioxide in a headspace. The three categories are: (1) lower than a range found to be useful for carbon dioxide levels; (2) in the useful range for carbon dioxide levels; and (3) higher than the useful range for carbon dioxide levels.

TABLE 4 Results at 8 days % CO₂ Ave % O₂ Ave Overall Gill Stem Range CO₂ % Range O₂ % Rating Whiteness Bacteria Color Elongation <5.0 4.2 17-20 17.9 3.6 4.4 3.0 3.4 3.5 5.0-9.0 6.8 14-17 15.9 4.2 4.2 3.1 3.5 4.1 >9.0 13.9  1-14 10.2 3.9 3.1 4.8 3.7 4.0 Traditional 1.1 19.9 19.9 1.0 1.0 1.0 1.0 2.0 Till

The following conclusions can be drawn with reference to Table 4, which uses the rating scale previously described in Example 1:

(1) A combination of carbon dioxide level in the range of 5-9% and oxygen level in the range of 14-17% yielded a best overall rating.

(2) Although a high range of carbon dioxide level gave excellent bacterial control, this high range exhibited a light brown discoloration of mushrooms, thereby causing a reduction in the color and overall ratings.

(3) A medium range of carbon dioxide level (5-9%) gave good control of stem elongation.

(4) A combination of low carbon dioxide level and high oxygen level yielded the lowest ratings in all parameters, except for whiteness. If color was used as the sole criteria of quality, a lower carbon dioxide level (<5.0%) would be desirable.

Example 3

Mushrooms were prepared and packaged as described above. Evaluations were made, and respiration gases were measured at 3, 4, 5, 6, 7, and 8 days post-processing. Table 5 below sets forth a summary of data at 8 days.

TABLE 5 8-Day Evaluation # of bags % % Overall Gill Stem tested CO₂ O₂ Rating Whiteness Bacteria Color Elongation 10 6.9 16.3 4.2 4.4 4.7 4.7 3.7 10 5.2 16.9 4.2 4.4 4.4 3.6 3.4

When carbon dioxide levels were allowed to rise above 5%, there was a tendency for mushrooms to turn off-white to light brown. Surprisingly, browning occurred to a slight degree, and other benefits associated with higher carbon dioxide levels outweighed the slight discoloration. As noted in Table 5, whiteness ratings were similar when categorized as under or above 6% carbon dioxide levels in a headspace. By allowing carbon dioxide levels to elevate above 6%, additional benefits were realized, such as improved bacterial control, improved gill color, and reduced elongation of stems.

Example 4

Hole patterns that performed well in other tests were tested gain. A comparison was made between bags with those hole patterns in terms of a distribution of holes in their upper portions (void volumes) and their lower portions (mushroom storage volumes). The bags had a total of 20-25 holes per bag. A comparison was also made amongst those bags with the same number of holes (20 holes). Mushrooms were harvested and processed as in previous examples, packaged in duplicate, and held at 38° F. through the duration of the tests. Unlike certain other tests in which 8 ounces of mushrooms were used, 10 ounces of mushrooms were packaged in each bag. Table 6 below illustrates the effect of hole location.

TABLE 6 Results at 8 days Holes in Total Ave. % CO₂ Ave. % O₂ headspace/over the Holes in in Std in Std. top of mushrooms Bag headspace Dev. headspace Dev. 4 20 9.6 ±4.3 13.1 ±3.4 22 22 9.7 ±0.5 13.7 ±1.5 8 20 8.5 ±2.4 14.6 ±2.0 10 20 9.9 ±0.9 13.6 ±0.9

Referring to Table 6, the following conclusions can be drawn:

(1) As expected, carbon dioxide levels were somewhat higher with two additional ounces of mushrooms per bag. At 8 days, the carbon dioxide levels averaged 8.5-9.9%.

(2) Significant overall browning of mushrooms occurred when carbon dioxide levels were above 9.0%.

(3) When a greater proportion of holes were in a lower portion of a bag in the vicinity of mushrooms, there was a greater variation in carbon dioxide level in a headspace. This effect may be due to coverage of the holes by the mushrooms, with a level of coverage varying from bag to bag based on locations of mushrooms within each bag.

Example 5

Table 7 below sets forth further results of tests that were performed.

TABLE 7 No. of Total holes in No. Gill Stem % % headspace of holes Overall Whiteness Color Elong. CO₂ O₂   4 holes 20 3.6 4.0 1.9 2.1 6.4 16.1 8-10 holes 20 3.7 3.8 2.6 2.8 6.1 16.3   4 holes 24-25 3.6 4.6 1.6 2.3 7.0 15.1 Till 2⅛ inch holes

Referring to Table 7, the following conclusions can be drawn:

(1) In general, excellent overall quality of mushrooms was maintained using bags. This is believed to be due to an elevated carbon dioxide level, which was between 5% and 9% in a majority of bags tested.

(2) Excellent quality was achieved in the presence of elevated carbon dioxide level (average 5.4%) and slightly reduced oxygen level (average 17.2%).

(3) Desirable hole patterns allowed headspace equilibrium to be achieved in less than 24 hr.

(4) Gill color and stem elongation were rated considerably higher in bags where about 50% of open area was in a headspace region.

(5) Excellent quality was achieved when at least 10 perforations were placed in a headspace of a bag, with no more than 4 perforations in a mushroom storage volume. This arrangement allowed carbon dioxide levels to reach between 5.0% and 9.0% over 8 days of shelf-life, as well as adequate moisture transfer from the bag.

Example 6

Mushrooms were harvested and prepared as described above. The results shown below relate to 8 ounce bags, although results for 10 ounce bags were similar. To simulate distribution conditions, the mushrooms were stored at 42° F. Composition of an atmosphere surrounding the mushrooms reached equilibrium within 24 hr, and a similar headspace trend was observed from day 1 through day 6.

TABLE 8 Results at 6 days Hole Gill Stem No. CO₂ O₂ Overall Whiteness Bacteria Color Elongation 24 5.4 15.3 3.4 3.4 3.0 2.6 2.5 20 8.4 14.2 2.3 2.7 2.0 2.5 2.9 6-8 15.0 9.1 2.5 1.8 4.4 3.1 4.0 Till 1.6 20.4 1.0 2.0 1.0 1.0 3.0 Control

Referring to Table 8, the following conclusions can be drawn:

(1) High carbon dioxide levels were observed to inhibit bacterial growth and to provide benefits in terms of gill color and stem elongation. However, the high carbon dioxide levels were also observed to produce undesirable discoloration of the mushrooms.

(2) Sufficient open area to provide 5-7% carbon dioxide and 14-17% oxygen yielded the best overall and whiteness ratings.

(3) 6-8 holes can maintain sufficient oxygen levels to avoid anaerobic conditions and the danger of botulism.

Example 7

During distribution, mushrooms can be exposed to higher than desirable temperatures. To confirm projected open area (or hole number) for this situation, mushrooms were harvested and handled as previously described and held at an elevated temperature of 42° F. A bag with 20 or 6-8 perforations was used to store 8 ounces of mushrooms, while a bag with 24 perforations was used to store 10 ounces of mushrooms. Table 9 below sets forth results at 5 days.

TABLE 9 5-Day Evaluation - Averages Overall Gill Stem Bag Design CO₂ O₂ Quality Whiteness Color Elong. 10 oz, 24 9.8 13.7 3.3 3.2 2.3 3.3 holes 8 oz, 20 7.7 15.2 3.0 3.0 2.6 3.9 holes 8 oz, 6-8 16.5 8.4 3.0 3.1 3.1 3.4 holes Till Control 1.3 20.3 2.0 2.5 1.0 3.0

Referring to Table 9, the following conclusions can be drawn:

(1) Quality of mushrooms within bags was superior to a till control.

(2) Relationship of hole number with respect to mushroom weight can affect quality. Even with an increased open area, carbon dioxide levels for 10 ounces of mushrooms can reach above a desired level.

(3) In the case of reduced open area, such as with 6-8 holes, carbon dioxide and oxygen levels in a headspace can reach undesirable levels from a food safety point of view. Also, high levels of carbon dioxide can cause an off-white to light brown discoloration of the mushrooms.

Example 8

For a number of reasons, the quality of mushrooms can vary within and over different harvests. Mushrooms were harvested and handled as previously described. In this example, good quality (at harvest) and inferior quality (at harvest) mushrooms were packaged in perforated bags, and compared with mushrooms of similar quality that were packaged in tills. All mushrooms were maintained at 38° F. Results were monitored over 5 days. To simulate commercial applications, 8 and 10 ounces of mushrooms were packaged.

In cases where carbon dioxide level was between 6% and 8%, the quality of bagged mushrooms was generally better, with overall ratings between 4.5 and 4.8 on a 5 point rating scale. The quality of whole mushrooms packaged in perforated bags at 5 days was similar in many aspects to the quality of whole mushrooms packaged in tills. However, due to a modified atmosphere, stem elongation was reduced in the bagged mushrooms with average ratings of at least ½ point over comparable mushrooms held in traditional tills. A greater difference was observed between the quality of sliced mushrooms held in perforated bags versus those held in traditional tills.

Benefits of a modified atmosphere for maintaining freshness of inferior quality (at harvest) mushrooms were greater than those for good quality (at harvest) mushrooms. The greatest impact observed was for gill color (in the case of whole mushrooms) and stem elongation. As in other examples, the benefits are believed to be at least partly associated with higher levels of carbon dioxide.

Example 9

Tests were performed to determine whether a shelf-life of unwashed mushrooms would benefit from a modified atmosphere and whether the unwashed mushrooms would exhibit, due to lack of exposure to water, improved shelf-life over that of washed mushrooms. Post-harvest handling of mushrooms was the same, but the mushrooms were not washed or treated with a browning inhibitor. Table 10 and Table 11 set forth results at day 8 and day 9, respectively.

TABLE 10 Example of benefits for unwashed mushrooms - Day 8 at 42° F. Pkg. Bag Overall Gill Stem Wt Design Rating Whiteness Bacteria Color Elong. Moisture CO₂ O₂ 10 oz 8 × 8 × 8 4.5 4.5 4.3 4.6 4.2 4 10.0 13.9 10 oz 10 × 10 × 10 4.5 4.5 4.3 4.3 4.0 3.9 6.9 16.3  8 oz 6 × 8 × 6 4.5 4.5 4.7 4.7 3.7 3.8 7.1 15.6  8 oz 8 × 8 × 8 4.5 4.5 4.1 4.1 4.0 3.8 6.8 16.4  8 oz Till 3.5 3.0 3.0 4 4.0 5 1.8 19.9

TABLE 11 Example of benefits for unwashed mushrooms - Day 9 at 42° F. Pkg. Bag Overall Gill Stem Wt Design Rating Whiteness Bacteria Color Elong. Moisture CO₂ O₂ 10 oz 8 × 8 × 8 4.2 3.7 4.1 4.2 4.2 3.7 11.3 12.7 10 oz 10 × 10 × 10 4.5 3.9 4.4 4.1 4.0 3.9 8.6 14.8  8 oz 6 × 8 × 6 4.5 3.5 4.3 4.1 3.8 3.6 9.5 14.4  8 oz 8 × 8 × 8 4.5 3.6 4.1 4.0 4.0 3.8 8.3 15.3  8 oz Till 1.0 3.0 1.0 3.0 4.0 5.0 1.9 19.9

Referring to Table 10and Table 11, the following conclusions can be drawn:

(1) Excellent quality was observed for bagged, unwashed mushrooms at days 8 and 9, whereas unwashed mushrooms in tills were no longer acceptable at day 9. The unwashed mushrooms in tills were given an overall rating of 1.0, whereas the bagged, unwashed mushrooms received an average overall rating of 4.5.

(2) The bagged, unwashed mushrooms received higher ratings versus those in a traditional till for each rated parameter.

(3) Carbon dioxide levels were lower (not shown) versus washed mushrooms, and in general fell within a desired range of 5%-9%.

(4) Compared with washed mushrooms, increasing a number of holes was observed to have a greater impact on levels of respiration gases for the bagged, unwashed mushrooms.

(5) Due to lack of exposure to water, the quality of the bagged, unwashed mushrooms was generally better versus washed mushrooms beyond 6 days.

Example 10

Tests were performed on bags formed of three different materials, namely polyethylene (PE), polyethylene terephthalate (PET), and high-clarity, polyolefin (Clysar® film). Bags of two sizes were used: (1) 40 ounce bags had 34 perforations (200 μm) per row and 4 rows per bag; and (2) 24 ounce bags had 25 perforations (200 μm) per row and 4 rows per bag. Sliced mushrooms were placed in the bags, and levels of respiration gases were measured in a headspace and a body portion of each bag. Table 12 below sets forth results at days 6, 7, and 8.

TABLE 12 Day 6 Day 7 Day 8 headspace Body headspace Body headspace Body O₂ CO₂ O₂ CO₂ O₂ CO₂ O₂ CO₂ O₂ CO₂ O₂ CO₂ 40 oz. PET 18.8 4.2 19.2 3.6 18.9 4.1 19.3 3.8 18.8 4.2 19 3.9 40 oz. PET 19.2 3.7 19.5 3.3 19 4.1 19.2 3.9 18.8 4.2 19 3.9 40 oz. PE 18.3 4.6 18.6 4.3 18.5 4.8 18.7 4.6 19.6 3.1 19.7 3 40 oz. PE 18.4 4.6 18.6 4.3 18.3 5 18.4 4.8 18.4 4.7 18.5 4.5 40 oz. Clysar 19.3 3.5 19.6 3.2 19.4 3.8 18 3.5 18 5 18.1 4.8 40 oz. Clysar 18.8 4.2 19.5 3.2 18.7 4.7 17.9 4.3 17.9 5.1 18.2 4.8 24 oz. PET 19.1 3.9 19.2 4.3 18.8 4.5 19.3 3.8 19.3 3.7 19.3 3.6 24 oz. PET 19 4.2 19.6 3.4 18.6 4.7 18.6 3.9 18.6 4.5 19.2 3.7 24 oz. Clysar 19.4 3.6 19.9 2.9 19 4.2 19 3.7 19 4.1 19.3 3.7 24 oz. Clysar 19.6 3.4 19.7 3.2 19.5 3.6 19.3 3.1 19.3 3.8 19.4 3.7

Levels of oxygen and carbon dioxide were generally comparable across bags of the same size but formed of different materials. However, polyolefin bags were superior in terms of a reduced amount of condensation observed at day 8.

Example 11

Tests were performed on bags formed of three different materials, namely polyethylene (PE), polyethylene terephthalate (PET), and high-clarity, polyolefin (Clysar® film). Bags of two sizes were used: (1) 40 ounce bags had 28 perforations (200 μm) per row and 4 rows per bag; and (2) 24 ounce bags had 18 perforations (200 μm) per row and 4 rows per bag. Sliced mushrooms were placed in the bags, and levels of respiration gases were measured in a headspace and a body portion of each bag. Table 13 and Table 14 below set forth results at day 3.

TABLE 13 Results at Day 3 headspace Body 40 oz. O2 CO2 O2 CO2 Clysar 17.2 7.1 17.9 6.2 Clysar 17.3 7.1 17.8 6.4 Clysar 17.4 7 17.7 6.5 Clysar 17.5 6.9 17.8 6.4 Clysar 17.9 6.3 17.8 6.4 PET 18.4 5.7 18.8 5.1 PET 18 6.2 18.5 5.4 PE 17.9 6.1 17.9 6.2 PE 17.8 6.4 17.7 6.4 PE 17.9 6.2 17.9 6.3

TABLE 14 Results at Day 3 headspace Body 24 oz. O2 CO2 O2 CO2 Clysar 17.2 7.4 17.7 6.5 Clysar 18.7 5.2 18.8 5 Clysar 17.9 6.2 18 6.1 Clysar 17.6 6.8 18.1 6.1 Clysar 17.7 6.7 17.8 6.4 Clysar 17.7 6.7 18.3 5.8 PET 18.5 5.2 18.2 5.1 PET 18.6 5.3 18.1 5.2

Levels of oxygen and carbon dioxide were generally comparable across bags of the same size but formed of different materials. However, polyolefin bags were superior in terms of a reduced amount of condensation observed at day 3. In particular, the polyolefin bags remained clear with very few water drops observed, while a greater amount of moisture saturation was observed for PET bags.

While the invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, process operation or operations, to the objective, spirit and scope of the invention. All such modifications are intended to be within the scope of the claims appended hereto. In particular, while the methods disclosed herein may have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the invention. Accordingly, unless specifically indicated herein, the order and grouping of the operations is not a limitation of the invention. 

1. A method for extending freshness of Agaricus bisporus mushrooms, comprising: providing a modified atmosphere in contact with Agaricus bisporus mushrooms, said modified atmosphere comprising from 14% to 18% by volume of oxygen and from 5% to 9% by volume of carbon dioxide.
 2. The method of claim 1, wherein said modified atmosphere comprises from 15% to 17% by volume of oxygen.
 3. The method of claim 1, wherein said modified atmosphere comprises from 6% to 8% by volume of carbon dioxide.
 4. The method of claim 1, wherein said modified atmosphere comprises from 15% to 17% by volume of oxygen and from 6% to 8% by volume of carbon dioxide.
 5. The method of claim 1, wherein said modified atmosphere has a relative humidity in the range of 87% to 100%.
 6. The method of claim 1, wherein providing said modified atmosphere includes: storing said Agaricus bisporus mushrooms within a container, said container having a plurality of holes that provide an air flow rate, per ounce of said Agaricus bisporus mushrooms, in a range of 0.2 to 0.6 Standard Cubic Foot per Hour when a pressure differential of 5 inches of water is applied.
 7. The method of claim 6, wherein said holes are oblong and have respective lengths in a range of 200 μm to 300 μm.
 8. The method of claim 7, wherein said holes have respective length-to-width ratios no greater than
 2. 9. The method of claim 6, wherein said holes are substantially circular and have respective diameters in a range of 150 μm to 600 μm.
 10. The method of claim 6, wherein said container has from 2 to 4 holes per ounce of said Agaricus bisporus mushrooms.
 11. The method of claim 6, wherein said container has from 2 to 2.5 holes per ounce of said Agaricus bisporus mushrooms.
 12. A container for storing Agaricus bisporus mushrooms, comprising: a set of walls defining an interior space and having a plurality of holes that are spaced to provide substantially even diffusion of respiration gases through said holes, said holes providing an air flow rate, per ounce of Agaricus bisporus mushrooms to be stored within said container, in a range of 0.2 to 0.6 Standard Cubic Foot per Hour when a pressure differential of 5 inches of water is applied.
 13. The container of claim 12, wherein said air flow rate is in a range of 0.3 to 0.45 Standard Cubic Foot per Hour.
 14. The container of claim 12, wherein said holes are oblong and have respective lengths in a range of 200 μm to 300 μm.
 15. The container of claim 14, wherein said holes have respective length-to-width ratios no greater than
 2. 16. The container of claim 12, wherein said holes are substantially circular and have respective diameters in a range of 150 μm to 600 μm.
 17. The container of claim 12, wherein said container has from 2 to 4 holes per ounce of Agaricus bisporus mushrooms to be stored within said container.
 18. The container of claim 12, wherein said container has from 2 to 2.5 holes per ounce of Agaricus bisporus mushrooms to be stored within said container.
 19. The container of claim 12, wherein said interior space contains a modified atmosphere comprising from 14% to 18% by volume of oxygen and from 5% to 9% by volume of carbon dioxide.
 20. The container of claim 12, wherein said interior space contains a modified atmosphere comprising from 15% to 17% by volume of oxygen and from 6% to 8% by volume of carbon dioxide. 